Radio receiver



Ap 26, 1949. L..COUILLARD RADIO RECEIVER 2 Sheets-Sheet 1 Filed Feb. 12,1943 INVENTOR Lou/s cal/141M)? April 26, 1949. CQUILLARD 2,468,041

RADIO RECEIVER Filed Feb. 12, 1943 2 Sheets-Sheet 2 O V snow/1v; SINGLEFREQ. F} 05011.44 TOR FOR THREE BAA/05 $055721 4 2771 fiARMa/v/c) HA NGEJANp 3 I 2 F2 [2 4 AMAma/wc} FREQ.

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3 B LOU/S C'OU/LL/IRD' BAND 2 O FREQ. ATTOR A/EY Patented Apr. 26, 1949RADIO RECEIVER Louis Couillard, Boulogne-Billancourt, France, assignorto International Standard Electric Corporation, New York, N. Y., acorporation of Delaware Application February 12, 1943, Serial No.475,685 In France March 9, 1942 .6 Claims. 1

The present invention relates to radio receivers employing frequencyconversion.

The arrangement of several variable frequency circuits, present in theusual heterodyne radioelectric receivers, has the following principaldisadvantages:

Since the difference between the frequency of the signal to be receivedand the frequency of the local oscillator must be constant, thearrangement of a single control usually renders it necessary to use acondenser with plates of a special shape. The use of a specially shapedcondenser for each Wave band to be received in order to maintain apredetermined constant intermediate frequency, is particularlyundesirable. Exact alignment of the circuits of the conventionalheterodyne receiver is usually dimcult. Harmonies of the intermediatefrequency which occur in the wave band of reception or harmonics of thelocal oscillator may cause unwanted heat frequencies with the carrier. I

Moreover, if the intermediate frequency is constant the signal frequencyapproaches the intermediate frequency, and the circuits may start tooscillate spontaneously thus impairing the reception of a signalcarrier, the frequency of which is in the neighborhood of theintermediate frequency. For this reason, frequencies in the neighborhoodof the intermediate frequency cannot be included in the reception bands.

The principal object of the invention is a heterodyne receiver in whichany received signal carrier regardless of frequency may never approachthe intermediate frequency, nor the local oscillator frequency, northeir harmonics or sub harmonics.

It is a further object of the invention to eliminate all disadvantagesmentioned above and to provide a receiver construction with a singlecontrol for all the variable circuits, in which an exact alignment ofthe tuned circuits and a perfect reception over an extended range ofsignal frequencies are obtained.

The objects of the invention are accomplished by means of thearrangement and combination of elements set forth in the specification,defined and illustratively exemplified in the accompanying drawings, inwhich Fig. 1 is a wiring diagram of the high and medium frequency stagesof a receiver with simple frequency conversion, that is, a receiverhaving a single intermediate frequency;

Fig. 2 is a wiring diagram of the high and medium frequency stages of areceiver with a double frequency conversion; 1

Fig. 3 is a set of curves illustrating the frequency changes in ordinarysuperheterodyne receivers;

Fig. 4 is a set of curves-illustrating the fre quency changes in areceiver of the present invention; and

Fig. 5 is a set of curves illustrating the positions of the harmonics ofthe local oscillator frequency with respect to bands of signalfrequencies.

In Figs. 1 and 2 of the drawings, only the elements of the receivers areshown which are necessary for an understanding of the invention.

Referring now to the drawings, and particularly to Fig. 1, Ll, C'ldenote the input circuit which is tuned to the frequency Fl of thesignal carrier wave. V! is a frequency converter tube. The localoscillation for the tube Vl is furnished by the tube V2 having anoscillating circuit L2, 02 tuned to the local frequency F2. The circuitL3, C3, which is the plate circuit of the tube Vl, is tuned to theintermediate frequency F3.

Obviously, any number of R. F. or I. F. amplifiers circuits may be tunedrespectively to the frequencies Fl and F3 without departing from thespirit and scope of the present invention.

The relation between the three frequencies Fl, F2 and F3 ispredetermined in accordance with the well known equations:

F2 =F1 :F3 when F3 is less than Fl. F2:F3:':F1 when F3 is greater thanF1.

According to the invention, the three condensers Cl, C2 and C3 are keyedto a common control shaft and have identical variation characteristics,and, furthermore, the proportion between their end values (inclusive ofthe residual capacity of the circuits) is the same. In Fig. 4 therelation of the various frequencies for-the case when the intermediatefrequency F3 is less than the signal frequency Fl has been illustrated.The curves have been plotted with frequency as the ordinate againstsignal frequency, Fl as the abscissa. The two possible local oscillatorfrequencies have been represented as curves F212 and F21), these beingthe upper and lower frequencies, respectively. This figure may becompared to Fig. 3 Which shows the relation of the same frequencies inan ordinary superheterodyne receiver where the intermediate frequency ismaintained constant.

Because of the arrangement of the condensers in the present inventionthe proportion between Fl and F3 is a constant, and we can write:

and by substituting in the first equation above, we obtain I F2=(K1:1)F3

3 The proportion between F2 and F3 is also a constant, and we can thuswrite:

In order to obtain an exact alignment of the circuits it is, therefore,sufficient to establish the tuned circuits in such a manner that Theharmonics of the intermediate frequency F3 can, then, not interfere withthe signal frequency Fl unless KI is an integer. In practice it issufiicient that this condition is fulfilled for only one point of thewave band-in order to be correct for all its points. Likewise,interferences due to the harmonics of the local oscillator are avoided,because the oscillator is tuned by means of a variable condenser keyedto the same control shaft as the condensers of the other circuits, andits frequency is accurately located at a point away from any harmonic ofthe intermediate frequency. For example, a harmonic of the range n willdiffer by about n kc./s. from the harmonic of the intermediate frequencyof the same range. Thus, it is easy to eliminate all interferencesbetween this harmonic and the signal.

In the case of a receiver having several wave bands, differentself-inductance coils LI may be inserted between the points A and B andcorresponding self-inductance coils L2 inserted between the points C andD for each wave band (see Fig. 1). In order to maintain an exactalignment of the circuits, it is sufiicient to adjust the value of theresidual capacity for each wave band, for instance by means of the smalladjustable condensers Cal and Q12 shown, in such a manner that aconstant proportion is maintained for the capacities corresponding tothe two end positions of the variable condensers for the circuits Ll,CI, CalL2, C2, Ca2and L3,C3.

The reception bands can be easily so chosen that the signal frequencynever approaches the intermediate frequency to a point where thereception could be disturbed. Moreover, the frequency range occupied bythe intermediate frequency may even be included in the reception band.

Assuming, for instance, that the intermediate frequency varies between500 Ice/.9. and 1500 kc./s., the two next adjacent subdivisions of thereception band could be from 333 lac/s. to 1000 lea/s. and from 1000ko./s. to 3000 kc./s., the former band being a case where F3 is greaterthan Fl. The values of the intermediate frequency corresponding to theextreme frequencies of said sub-bands are given in the following table:

First band Second band Signal frequency (Fl) 333 1,000 1,000 3,000Intermediate frequency (F3) "A- 500 1,500 5.00 1,500

It will be seen that the frequency range occupied by the intermediatefrequency overlaps or passes through the signal frequency range withoutcausing any disturbance.

A receiving system according to the invention is particularly suitablefor the construction of a receiver with several successive frequencychanges, each subsequent converter frequency being lower than thepreceding one. In this case it is advantageous to select the differentfrequencies so that each higher local frequency is a multiple of thelowest local frequency. This makes it possible to use a singleoscillator and to utilize the fundamental frequency and the harmonics ofsaid oscillator for the different frequency changes. Curves illustratingthis feature are shown in Fig. 5.

Fig. 2 illustrates diagrammatically a receiver of this type. A highfrequency input circuit Ll, Cl, tuned to the frequency Fl of the signal,excites the first frequency converter tube VI. The local oscillation forthe tube Vl is furnished by an oscillator tube V2 through an oscillatingcircuit tuned to the first local frequency F2. The circuit L3, C3 forthe first intermediate fre quency F3 feeds the oscillations coming fromthe stage VI to a second frequency converter stage V3. The localoscillation for the stage V3 is furnished by the circuit L4, 04 tuned tothe second local frequency F4. The circuit L5, C5 is tuned. to thesecond intermediate frequency F5. In the example given, the circuit L2,C2 serves to filter the harmonic nFfl of the oscillator V2. Thus:

Adopting the same relations between the frequencies FI,F2 and F3 asinFig. 1:

The conditions for an exact alignment of the circuit are, then,expressed by the following equations:

Substitut g or F4 in the equation F2=nF4 we get These equations permitthe determination of the characteristics of the essential circuitelements in devices according to the present invention.

Instead of using harmonic frequencies as local frequencies, it ispossible to construct receivers with multiple frequency change and exactcircuit alignment by keying all the variable condensers to the samecontrol shaft; however, this arrangement involves certain materialdifficulties.

In a communication receiver with double frequency change, the amplifierfor the second intermediate frequency comprises generally a certainnumber of circuits which operate on a relatively low frequency.Therefore, the process according to the invention requires aconsiderable number of variable condensers of large capacity. On theother hand, the number of circuits for the first intermediate frequencyis relatively small, because their function is practically limited tothe elimination of the frequency image. The tuning of these firstintermediate frequency circuits by means of variable condensers keyed tothe same control shaft as those of the high frequency circuits, asprovided according to the invention, will-thus easily permit an exactalignment of the latter.

Carefully shaping the variable tuning condensers of the secondintermediat frequency circuit to obtain alignment over the tuning range,permits the omission of the so-called padding condensers from theoscillator circuits of all the sub-bands. The suppression of allinterrferences between the signal and the harmonics of the localoscillations and of the first intermediate frequency is insured. As faras the sec- 0nd intermediate frequency is concerned, it can be chosensufiiciently remote from the first one to render its harmonics harmless.As shown in detail with respect to the receivers with simple frequencyconversion, it is also possible to have reception over a continuousfrequency band which may include the first and th second intermediatefrequency Without any inconveniences due to the closeness of the signalfrequency and the intermediate frequency.

It will be understood that the invention is not limited to theembodiments shown and described, but may be carried into effect bynumerous other arrangements or modifications.

I claim:

1. Radio receiver with multiple frequency conversion comprising aplurality of converter tubes, each tube having an input circuit, a localoscillator circuit, and an intermediate frequency circuit, each of saidcircuits including a separate variable tuning condenser, all said tuningcondensers having identical variation characteristics and the sameproportions between their end values inclusive of the residualcapacities of the circuits, a common control shaft to which all saidvariable tuning condensers are keyed, and an oscillator, said oscillatorbeing coupled to the local oscillator circuits of each of said convertertubes, said local oscillator circuits being resonant to differentfrequencies so that each subsequent conversion frequency is lower thanthe preceding one.

2. Radio receiver, as claimed in claim 1, in which the resonantfrequency of the oscillator circuits are multiples of one another.

3. Radio receiver, as claimed in claim 1, wherein, the resonantfrequencies of said oscillator circuit are, respectively, thefundamental frequency and the harmonics of said oscillator.

4. Radio receiver with multiple frequency conversion comprising aplurality of converter tubes coupled in cascade, each tube having aninput circuit, a local oscillator circuit, and an intermediate frequencyoutput circuit, each of said circuits including a separate variabletuning condenser, all said tuning condensers having identical variationcharacteristics and the same proportions between their end valuesinclusive of the residual capacities of the circuits, a common controlshaft to which all said variable tuning condensers are keyed, a singleoscillator, the local oscillator circuit of one converter tube beingresonant to the fundamental frequency of said oscillator and the localoscillator circuit of a succeeding converter tube being resonant to aharmonic of said oscillator.

5. Radio receiver as claimed in claim 4, in which, for the reception ofa given signal frequency, the capacities of said variable tuningcondensers are defined by the following equations:

Where C1 is the capacity of the variable condenser in the first inputcircuit, C2 and C3, respectively, are the capacities of the variablecondensers in the first local oscillator circuit and in the firstintermediate frequency circuit, C4 and C5, respectively, are thecapacities of the variable condensers in the second local oscillatorcircuit and in the second intermediate frequency circuit, and n is therange of the oscillator harmonic used in said second oscillator circuit.

6. A superheterodyne radio receiver comprising a first frequencyconverter stage with an input circuit and an output circuit, a secondfrequency converter stage with an input circuit and an output circuit,the output of the first stage being coupled to the input circuit of thesecond stage,

' an oscillator, said oscillator having at least two resonant circuits,one oscillator circuit being resonant to a harmonic frequency of theother oscillator circuit, said resonant circuits being coupled,respectively, to the first and to the second converter stages, separatemeans for tuning said input and output circuits of the converter stagesand the oscillator resonant circuits, and mechanical interlocking meansbetween the separate tuning means for adjusting the tuning means inunison.

LOUIS COUILLARD.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,342,885 Armstrong June 8, 19201,742,773 Loewe Jan. 7, 1930 1,933,778 West Nov. 7, 1933 2,020,832Grimes Nov. 12, 1935 2,086,331 Holmes July 6, 1937 2,151,810 SiemensMar. 28, 1939 2,186,980 Lowell Jan. 16, 1940 2,239,756 Riddle Apr. 29,1941 2,282,092 Roberts May 5, 1942

